Trucks and other heavy vehicles have not traditionally been known for offering a smooth, comfortable ride. Quite to the contrary, most trucks and other heavy vehicles do not sufficiently cushion the bumps and contours of the road and the vehicle, load, and driver must absorb the shocks and impacts of traveling on rough or bumpy pavement. This inability to provide adequate cushion from the bumps and roughness of the road leads to increased wear on vehicle parts resulting in increased maintenance. Further, damage to the vehicle's load may occur if the load is fragile or the bumps severe. Perhaps more important, this inability to adequately cushion the ride can lead to serious safety problems such as driver fatigue and vehicle mishandling.
Most trucks and other heavy vehicles use leaf spring suspension systems for cushioning the front steering axle of the vehicle. FIG. 1 depicts a typical leaf spring suspension system used on the front steering axle of a heavy vehicle (not shown). The axle 10 is bolted or otherwise attached to the central and thickest portion of a leaf spring stack 12. One end 14 of the leaf spring stack 12 pivotably attaches to the frame of the vehicle through a fitting 16 which requires regular maintenance including greasing. Typically, the other end 18 of the leaf spring stack 12 connects to the frame through a frame shackle similar to the fitting 16 and shock absorber (not shown) for dampening. Leaf spring suspension systems are heavy, require regular maintenance, and do not provide a smooth ride. Additionally, the cost of leaf spring stacks, which usually must be replaced every several years, can be quite high.
The use of air suspension systems in connection with the rear axles of trailers, tractors, dump trucks, and other heavy vehicles is well known in the art. Attempts to adapt such air suspension systems for the front steering axle of heavy vehicles have not proven successful because of the complexity of the moving parts involved in such systems, and the time and expense associated with replacing complicated parts. Air suspension systems typically offer a significantly better ride than leaf spring systems but require more space to install and generally require a much higher degree of maintenance especially due to the use of multiple grease fittings. One such system, disclosed in U.S. Pat. No. 4,181,323, uses four such grease fittings for a single-axle suspension and eight such fittings for a dual axle suspension and is thus, not a good solution.
Accordingly, there is a need for a low maintenance, high shock absorption, suspension system that can be used in connection with the front steering axle of trucks or other heavy vehicles. Further, it would be desirable if the suspension system weighed less than leaf spring systems, did not use any high-maintenance grease fittings, could keep the front of the vehicle level at all times, provided a smooth ride with less vibration than existing systems, had few moving parts to wear out, and stabilized the vehicle under extreme loading conditions.